1. Field of the Invention
The present invention relates to an electronic component in which an electronic component element, such as a surface acoustic wave element or a semiconductor element, is electrically and mechanically joined to a base member via bump bonding.
2. Description of the Related Art
As electronic components in which electronic component elements are mounted on base members by bump bonding, a surface acoustic wave device has been known, for example, which has the structure shown in FIG. 8. In this surface acoustic wave device, a surface acoustic wave element 20 is electrically and mechanically bonded to a base member 10. While a propagation surface of the surface acoustic wave element 20 is opposed to the base member 10, input/output electrode pads 25a and 25b and an electrode pad for grounding 25c of the surface acoustic wave element 20 are respectively joined to corresponding input/output electrode pads 12a and 12b and an grounding electrode pad 12c of the base member 10 via bumps 51a to 51c which are formed of a material such as Au. Each of the bumps 51a to 51c is formed to have the same height. Then, a cap member 30 is joined to the base member 10 so as to cover the surface acoustic wave element 20, so that the surface acoustic wave element 20 is hermetically sealed within a package defined by the base member 10 and the cap member 30.
However, in a conventional surface acoustic wave device, when a mechanical stress such as an impact caused by dropping the device or a thermal stress such as variation in ambient temperature is applied thereto, mechanical damages such as fracture and exfoliation are produced in bumps 51a and 51b and electrode pads 25a and 25b which are respectively bump-bonded thereto. Such mechanical damage usually occurs in a peripheral portion of the base member 10 and the surface acoustic wave element 20, and the failure in the bump bonding process causes the electronic device to have faulty characteristics. This is because the damage caused by the mechanical stress or the thermal stress is often concentrated on bumps located along a peripheral portion instead of bumps located at the central portion.
In order to overcome the problems described above, preferred embodiments of the present invention provide an electronic component wave device which achieves a high degree of reliability and prevents problems and faulty connections conventionally occurring during bump bonding by relieving the stress applied to the bumps located along a peripheral portion of a base member and an electronic component element.
According to a preferred embodiment of the present invention, an electronic component includes a base member having a plurality of electrode lands, an electronic component element having a plurality of electrode pads and being electrically and mechanically joined to the base member, a plurality of bumps located between the electronic component element and the base member, the plurality of electrode pads of the electronic component element and the corresponding electrode lands of the base member being respectively joined together via the bumps such that the electronic component is opposite to the base member, wherein the bumps located at the peripheral portion of the electronic component element have a greater height than that of the bumps located in the central portion of the electronic component element.
As a result of this unique structure, the stress applied to the bumps located at the peripheral portion is relieved because the bumps located at the peripheral portion, in which the stress is prone to concentrate, have a greater height than that of the bumps located in the central portion. Consequently, bonding problems such as damage to electrodes or bump bonding portions and exfoliation are reliably prevented, resulting in improved reliability of the electronic component.
In order to obtain bumps having a greater height at the peripheral portion than that of the bumps located at the central portion, various methods such as changing the film thickness of electrode lands formed on the base member; forming the base member to have a convex shape; forming the base member to have a curved shape; or changing the film thickness of electrode pads of the surface acoustic wave element, may be used. Also, any combination of these methods may also be used.
In the above-mentioned configuration, it is preferable that the differences between heights of the bumps are about 1 xcexcm to about 10 xcexcm.
In addition, preferred embodiments of the present invention provide an electronic component in which a surface acoustic wave element or a semiconductive element, or other suitable electronic component element, is electrically and mechanically joined to a base member via bump bonding.
According to preferred embodiments of the present invention, the bumps located at the peripheral portion, in which the stress is prone to concentrate, have a greater height than that of the bumps located at the central portion so as to relieve the stress applied to the bumps located at the peripheral portion, so that bonding problems such as damage to electrodes located at bumps or bump bonding portions and exfoliation are reliably prevented.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.